1. Field of the Invention
The present invention relates to a push button switch provided with a multistage actuation interlock function for actuating a plurality of switches at multiple stages, which is suitable for use to control a motor for driving a hoist, a chain block, etc. at a plurality of stages of speed.
2. Description of the Prior Art
The push button switch provided with a two-stage actuation interlock function used for reversibly rotating a motor for driving a hoist, a chain block, etc. has been already disclosed in JP-Y-4-31686. The prior art push button switch as described above is provided with an interlock plate pivotally supported by a fixed axle, and a pair of movable bodies for actuating each of both ends of the interlock plate. An upper end of each of the movable bodies projects out of a casing so as to function as a push button. Each of the movable bodies is formed with a recessed portion on both side portions thereof, respectively. Further, a lid body is formed with a stepped portion in correspondence to the recessed portion, respectively. Further, a mutually-operative bearing and spring assembly is provided at the corresponding recessed portion and the stepped portion, respectively. Since the prior art push button switch is constructed as described above, it is possible to realize a push button switch provided with a two-stage switching function.
Here, when a three-stage push button switch is required to be constructed on the basis of the structure which is basically the same as the above-mentioned prior art push button switch provided with the two-stage actuated interlock plate, the size of the push button switch inevitably increases, as shown in FIGS. 1(A) to 1(D).
In more detail, with reference to FIGS. 1(A) to 1(D), an internal space of a casing 1 is divided symmetrically into right and left sides, and an interlock plate 16 is pivotally provided so as to be pivotal about a fixed axle 17 mounted horizontally at the middle bottom portion of the casing 1. A pair of push buttons 20a and 20b movable in the vertical direction are arranged so as to project out of the upper portion of the casing 1. Under the lower end of each of the push buttons 20a and 20b, a movable body 21a or 21b is attached, respectively. Whenever the push button 20a or 20b is actuated, the interlock plate 16 is pivoted by being pushed by the movable body 21a or 21b. Each of the movable bodies 21a and 21b has one set of three movable contacts 18a, 18b and 18c, respectively. On the other hand, on the bottom surface of the casing, one set of three fixed contacts 19a, 19b and 19c are provided so as to be opposed to the three movable contacts 18a, 18b and 18c, respectively. Therefore, whenever the push button 20a or 20b is depressed, these three movable contacts 18a, 18b and 18c are closed (turned on) so as to contact the fixed contacts 19a, 19b and 19c selectively in sequence according to the stroke of the push button 20a or 20b. Here, a pair comprising the movable contact 18a and the fixed contact 19a constitutes the first stage contacts; a pair comprising the movable contact 18b and the fixed contact 19b constitutes the second stage contacts; and a pair comprising the movable contact 18c and the fixed contact 19c constitutes the third stage contacts. Movable contacts 18a to 18c are provided with a contact spring 22 (shown in FIG. 1(A)), respectively, to obtain a predetermined respective contact pressure.
FIG. 1(A) shows the state where the two push buttons 20a and 20b are both not depressed so that the push button switch is completely turned off. FIG. 1(B) shows the state where the first button 20a is depressed so that the pair comprising the first-stage movable contact 18a and the fixed contact 19a are in contact with each other. FIG. 1(C) shows the state where the first button 20a is further depressed deeper so that the pair comprising the second-stage movable contact 18b and the fixed contact 19b are in contact with each other in addition to the first-stage movable and fixed contacts 18a and 19a. FIG. 1(D) shows the state where the first push button 2a is furthermore depressed deeper so that the pair comprising the third-stage movable contact 18c and the fixed contact 19c are in contact with each other in addition to the first- and second-stage movable and fixed contacts 18a, 18b and 19a, 19b (all pairs of the movable and fixed contacts are in contact with each other only on the side of the push button 20a).
As is well-understood with reference to FIGS. 1(A) to (D), when the third-stage contact pairs are required to be closed to each other completely, since the push button 20a must be depressed deeply in the downward direction, the interlock plate 16 is inevitably pivoted clockwise through a large angle by the movable body 21a, with the result that there exists a problem in that the size of the entire push button switch inevitably increases.